Styrene-based resin is widely used as a general purpose resin because it is characterized in that it has a high rigidity, good appearance and is excellent in dimensional stability, and is low in water absorbance. However, the styrene-based resin is insufficient in chemical resistance, abrasion resistance and heat resistance and, in severe conditions, its use is restricted. On the other hand, crystalline thermoplastic resin compositions, especially, polyamide resin are widely used as an engineering plastic since it is excellent in chemical resistance, abrasion resistance and heat resistance, but it has a high water absorbance, and is not sufficient in rigidity and dimensional stability.
Under such a circumstance, resin compositions which have respective advantages of the styrene-based resin and the polyamide resin have been investigated, for example, a blend composition of an ABS resin, which is a representative styrene-based resin, and a polyamide resin is proposed. However, a simple blend of an ABS resin and a polyamide resin has problems that its mechanical properties are very low since their compatibility is inferior.
Under these circumstances, as a method for improving compatibility of ABS resin with polyamide resin, a method in which a monomer with a functional group which has an affinity to the polyamide resin is graft copolymerized to a rubbery polymer, and this graft copolymer is blended to the polyamide resin, is being investigated, and as one method thereof, a blend composition of a graft copolymer, in which an α,β-unsaturated carboxylic anhydride is graft copolymerized together with other monomer to a rubbery copolymer, and a polyamide resin is proposed. However, in the resin composition obtained in such a way, there are problems that it is insufficient in surface appearance, flowability and heat stability.
In addition, a blend composition of a graft copolymer, in which an unsaturated carboxylic acid amide together with other polymer is graft copolymerized to a rubbery polymer, and a polyamide resin is also proposed. However, this composition is insufficient in impact resistance and, furthermore, there are problems in surface appearance and mechanical properties when water is absorbed.
In such a circumstance, for the purpose of improving mechanical properties when water is absorbed, a resin composition comprising three components, in which a copolymer comprising an aromatic vinyl and an α,β-unsaturated carboxylic anhydride is used as a compatibility improver for the styrene-based resin and the polyamide resin, is proposed (for example, refer to the patent reference 1). However, this resin composition is insufficient in impact resistance at low temperature, flowability and surface appearance which are required when applications to interior or exterior materials for automobiles or housing, parts or the like of electric and electronic devices are desired.
For the purpose of improving impact resistance, for example, a resin composition in which a low molecular weight copolymer comprising an aromatic vinyl and α,β-unsaturated carboxylic acid and/or α,β-unsaturated carboxylic anhydride are added to the styrene-based resin and the polyamide resin, is proposed (for example, refer to the patent reference 2). However, this resin composition in which vinyl cyanide-based monomer is not contained in the above-mentioned copolymer was insufficient in impact resistance at low temperature and surface appearance.
On the other hand, a resin composition of which impact resistance is further improved by adding a styrene-acrylonitrile-maleic anhydride copolymer, having a maleic anhydride content of 0.3 to 1.5 mol % and an weight average molecular weight of about 40,000 to about 200,000, to ABS resin and polyamide resin is proposed (for example, refer to the patent reference 3). However, by adding the styrene-acrylonitrile-maleic anhydride copolymer of such molecular weight range, a resin composition which has an impact resistance at low temperature, flowability and surface appearance in good balance could not be obtained.
Furthermore, in order to improve impact resistance at low temperature, a resin composition of which impact resistance is further improved by adding styrene-acrylonitrile-maleic anhydride copolymer having an weight average molecular weight of 160,000 to about 230,000 to ABS resin and polyamide resin is proposed (for example, refer to the patent reference 4). However, with respect to this resin composition, too, by adding the styrene-acrylonitrile-maleic anhydride copolymer of such molecular weight range, flowability and surface appearance, especially, surface glossiness was not sufficient for the above-mentioned application.
In order to obtain a resin composition excellent in balance of impact resistance and flowability, a resin composition in which an agglomerated rubber, in which a small particle rubber of a specified particle diameter is agglomerated by compounding α,β-unsaturated carboxylic acid containing a copolymer of a specified reduced viscosity, for example, by compounding a styrene-acrylonitrile-methacrylic acid copolymer, is used, is reported (for example, refer to the patent reference 5). However, with respect to this resin composition, although flowability is improved, impact resistance and surface appearance, especially, surface glossiness was still insufficient for the above-mentioned application.
A resin composition in which a polyamide resin and a copolymer containing α,β-unsaturated carboxylic acid and/or α,β-unsaturated carboxylic anhydride are added to a styrene-based resin containing a rubber is disclosed (for example, refer to the patent reference 6). However, since it is intended in this invention to obtain a resin composition excellent in transparency, the aromatic vinyl monomer content contained in the rubber reinforced styrene-based resin is kept small and the impact resistance at room and low temperatures was inferior.
[Patent reference 1]JP-A-S60-195157[Patent reference 2]Specification of EP-A-0068132[Patent reference 3]Specification of U.S. Pat. No.4713415[Patent reference 4]Specification of U.S. Pat. No.5756576[Patent reference 5]JP-A-2000-17170[Patent reference 6]JP-A-2004-300354